Magnetic field sensors have many applications, one of which is automobile engine management applications. For example, magnetic field sensors associated with rotating tooth or pole wheels and a back bias magnet can be used to sense rotation and/or positioning of the camshaft.
To reduce engine emissions, more accurate control of the engine is desired. This can be provided, at least in part, by better-performing, more accurate sensors, such as those which provide improved output switching and are less dependent on the relative positioning of the sensor and the rotating element, as the sensor signal depends on both the strength of the magnetic field and the distance between the sensor and the target element.
Conventional solutions for determining output switching thresholds typically are reactive, based on a slow regulation as a reaction to current signal characteristics. One of two approaches generally is taken: to set a single threshold over the entire pattern with slow adaptation after an overall pattern change (slow reactive algorithm), as shown in FIG. 1A; or to continuously adapt according to the last pair of a signal maximum and a signal minimum (fast reactive algorithm), as shown in FIG. 1B. While these approaches can improve phase repeatability and run-out (i.e., wobble of a tooth or pole wheel not centered on an axis), and robustness (amplitude modulation), respectively, they offer sub-optimal phase accuracy. Moreover, and referring to FIG. 2, a conceptual diagram of a conventional sensor signal processing system, which can be used for the camshaft example mentioned above, is depicted. The point where the output changes state is defined by the amount of feedback signal provided by the offset regulation loop. The slow loop response, determined by an anti-aliasing filter present in the forward signal path (analog signal processing block), constrains the amount and the timing of the updates in the offset regulation loop to preferably rare small updates. This slow response can lead to parasitic switching, which is undesired.
Therefore, a need exists for improved output switching systems and methods.